Electrical control circuit



Jul zs, 1939. V H, BEL R 2,167,062

ELECTRICAL CONTROL CIRCUIT Filed Dec. 24, 1937 2 Sheets-Sheet 1 v GT1 22 g 0 H m 7 i 57 7 I]??? M L 1'! I 3nvntor July 25, 1939. H. BELAR v 2,167,062 7 ELECTRICAL CONTROL CIRCUIT Fil ed Dec. 24, 1957 l 2 Sheets-Sheet 2 vv v /9 H 7 I 1' I v 1 x Z5 7 I- h I Z 45 Zhwentor Patented July 25, rate ELECTRICAL con'rnor. cmcui'r Herbert Belar, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application December 24, 1937, Serial No. 181,588

6 Claims.

This invention relates to electrical circuits such as are utilized to control the amplification of different signal channels, the fading of one signal channel to another and the mixing of the outputs of associated signal channels. It has for its principal object the provision of an improved system and method of operation whereby these various results may be achieved without the dimculties heretofore incident to their realization.

As applied to the gain control of difierent signal channels, the improved system affords a ready means of controlling the gain of a plurality of channels either together or individually without undesirable interaction between the different channels. It also makes feasible such gain control from a plurality of diiferent points'such as a projection booth and a theater auditorium or the like.

-As applied to fading from one signal channel to. another, the improved system affords a simple means of changing from one channel to another whether the channels be utilized in connection with sound motion picturerecording..

sound motion picture reproducing, a radio broadcast station or the like.

As applied to the mixing of the outputs of different signal channels, the improved. system is especially applicable to sound recording, radio broadcasting and the like. i

An additional featureof the improved system is the provision of means for preventing interaction between two channels which feed into a single output or mixer stage.

.The invention will be better understood from the following description considered in connection with the accompanying drawings and its scope is indicated by the accompanying claims.

Referring to the drawings:

Figure 1 illustrates a modification of the invention wherein a pluralityof signal channels are arranged to have their gains controlled either independently or simultaneously and. are provided with means for readily fading from one of the channels to the other,

The arrangement of Fig. 2 is similar to that of Figure 1 except that provision is made for.

controlling the gain of the signal channels from different locations,

Figure 3 illustrates a modified form of thearrangement of Fig. 2, v v

Figure 4 illustrates a p1urality.of signal chan-- nels which are arranged to fade into a single output or mixer stage, are provided with means for preventing interaction between thediiferent signal channels, and with gain control and fading means similar ,to'those of the previous figures, and

Figure 5 is a wiring diagram illustrating certain details of the circuit of Fig. 4.

,The system of Fig. 1 includes a plurality of signal channels represented by the electron discharge devices i and H. These channels are respectively provided with the usual signal input circuits i2 and i3. Bias potential for controlling the gain of the two signal channels is derived from' a potential source and a potential source l which is shunted by a resistor it provided with an adjustable terminal I'l. Connected at the positive terminal of the battery it and the adjustable terminal ll are a resistor it provided with an adjustable terminal l9 and a resistor 20 provided with an adjustable terminal 2i, a switch 22 being provided in the high potential connection .of the resistor l8 and a switch 22 being provided in the high potential terminal of the resistor 2ll. Interposed between the input circuit i2 and the adjustable terminall9 and resistor I8 is a resistor 24. Similarly interposed between the adjustable terminal 2i and the resistor 20 and the input circuit I3 is a resistor 25.

7 It will be readily understood that the output circuits 26' and 21 of the devices i0 and ii may be connected through additional stages to auti- .lization device such as the loudspeaker of a sound motion picture reproducing equipment.

In the operation of the channels Iii and H the gain of the channel I0 is individually controlled by adjustment of the terminal I! of the resistor 18, the gain of the channel II is individually controlled by adjustment of the terminal 2| of the resistor 20 and the gains of the two channels are simultaneously controlled by adjustment of the terminal I! of the resistor it. Assuming the switches 22 and 23 to be closed and both channels to be in operation, the signal is faded from thechannel illto the channel i i by opening of the switch 22 which functions to -increase the negative bias potential applied to the control grid of the device i0, thus closing this device to the signal. Similarly, the signal is faded from the device II to the device ill by opening the switch 23 which increases the negative bias applied to the input circuit of this device.

Fig. 2 lllustratesa system which is similar to that of Fig. 1 but differs therefrom in that provision is made for controlling thegains'of the two channels from diiferent locations, such, for example, as the projection booth and auditorium of a sound motion picture theater. In this figfrom another point by the resistor 23.

2 g ure corresponding parts are indicated bythe same reference numerals. as--in Fig. 1. Potential for controlling the bias of the input-circuits l2 and I3 is derived from the battery l4 through resistors "and 29 in the case of the device'il and through resistors 30 and ii in the case of device II. The gain of the device it may be other point by the resistor 30. As will be readily understood, the resistors 28 and "may be located in a mo ion picture projector booth and the resistors 33 and 3i may be located in the auditorium. It will be noted that the range of control possible at the resistors and 33 is dependent on the position of the adjustable terminal of the resistor 23. This, of course, results in a somewhat limited control at one of the control points.

By connecting the resistors 28 and 23 in a closed loop or circle such as the resistor 32 of Fig. 3 equal freedom of control points may be realized. This arrangement, of course, involves the connection of a considerable numberof leads between the two points. In the projection booth, for example, a contact member 33 connected to the lower terminal of the resistor 24 is rotated to engage the various contacts of the resistor 32-and applied to the input circuit II. A bias potential which is variable from that point located in the auditorium'may be a rotatable insulation arm 34 provided at its opposite ends with brushes 33 and 36 arranged to engage a plurality'of contacts similar to those of the resistor 31 and to apply to v the engagedcontact the potential "of the source M. It thus follows that the arm 34 may be moved to advance the axis at which the potential of the source I4 is applied to the resistor 32 and that the member 33 may be moved to select any desired partof this-potential. 'This, of

course, makes possible at either location freedom in the control of the gain of the device I 0. It

should be noted that the arrangement of Fig. 3

may be duplicated in the same manner as'the arrangement of Fig. 2 for the purpose of controlling the gain of more than one channel and may also be provided at suitable points with the fading switches 22 and 23 of Figs. 1 and 2. Y a

The system of Fig. 4 illustrates the channels or devices II and II as arranged to feed into a single output channel orstage 31. It will be noted that the device III is coupled to the input circuit I of the device 31 through a capacitor 38 and that the device II is similarly coupled to this input circuit through a capacitor 39. In order to per-- fect interaction between the operation of the device I. and that of the device il, resistors 40 and 4| are connected in series between the capacitors 3. ancl 39 and are ..provided with an intermediate terminal from which the mixedsigas] is applied to the input circuitof the device 31. As in the previous modifications of the invention the gain-of the device I I is controlled through the resistor IS, the gain of the device ll is controlled through the resistor 20- and the gains of the devices I0 and 'ii are simultaneously .controlled through vthe resistor it. Otherwise For fading from the device It to the device ll a three position switch 43 is provided. In the and transfers the signal to the device ll.

illustrated position of this switch both thejdevice II and the device ii are arranged to supply to the input of the device 31- a mixed output which is dependent on the adjustment of the resistors I! and 20. Movement'of the switch 43 into enwith the contact 43 transfers the signal from the device II to the device ll. 1

The arrangement for preventing the operation of one of the devices from affecting the operation,

of the other is indicated somewhat more clearly in Fig. 5. It will be understood that the function of the resistors 43 and 4| is to present to the output circuit of the two devices an impedance which effectively isolates the one from the other.

It is evident that the arrangement of Fig.4 may be provided with either the circuit of Fig. 2 or the circuit of Fig. 3 where it is desired to control the different channels from diiferent. locations,

'the showing of this feature in connection with Fig. 4 being omitted to simplify an understanding 'of the invention.

I claim as my invention:

1. The combination of a plurality of signal channels, a single signal channel provided with an input circuit. impedance means interposed between the outputs of said plurality of channels for-preventing interaction therebetween and for applying to said input circuit a control potential dependent on the'combined outputs of said plurality of channels, means for independently adjusting the gain of said plurality of-channels and oi said single channel, and means for simulta-. neously adjusting the gain of all of said channels.

2. The combination of a plurality of signal" channels, a single signal channel provided with aninput circuit, impedance means interposed between the outputs of said-plurality of channels for preventing interaction therebetween and for applying to said input circuit a control potential dependent on the combined outputs of said plurality of channels, means for independently adjusting the gain of saidplurality -of channels I and .of said single channel, means for simultaneously adjusting the gain of all of said'channels, and means for fading from one to another of said plurality of signal channels. 4

3. The combination of a plurality of signal channels, means including a bias potential source and a plurality of resistors connected in parallel to said source for independently adjusting the gains of said channels, and means including a resistor connected to a part of said source and provided with a contact connected to the low potential terminal of each of said parallel resistors for simultaneously adjusting the gain of said channels. v

4. The combination of a plurality; of, signal channels, means including a bias potential source and a plurality of resistors connected in parallel to'said source for independently adjusting the gains of said channels, means including a re- I sistor connected to a part of said source and-provided with a contact connected to the low potential terminal of each of said parallel resistors for simultaneously adjusting the gain of said channels, and means for interrupting the high potential. terminal of each of said parallel resistors for fading from one'of said channels to another.

5. The combination of a plurality of signal channels, means including a bias potential source and a plurality of resistors connected in parallel to said source for independently-adjusting the gains of said channels, means including a resistor connected to a partof said source and provided with a contact connected to the low potential terminal of each of said parallel resistors for simultaneously adjusting the gain of said channels, and means for controlling the gain of said amplifiers from a plurality of different points.

6. The combination of a. plurality of signal channels having respective input circuits, means for independently controlling the transmission in each inputcircuit, means for simultaneously t controlling the transmission in all of said input circuits, and means individual to each of said signal channels for .fading from one to another of said signal channels. v

HERBERT BELAR. 

